very easy method .... right click on drive (where your database saved, i.e d:\ drive), select properties then

click on security - click on "everyone" then select 'full control' .... now stop - start your sql

if there is not available "everyone" then

click edit - click Add - click Advance - click on 'Find Now' button - select "everyone" in search result - click ok - then select "full control" in permission for everyone ....